2009 Vehicle Dynamics and Control Seminar Characterisation of Longitudinal Response for a Full-Time Four Wheel Drive Vehicle Jas Pawar (EngD Research Student) Sean Biggs (Project Supervisor & Principal Technical Specialist) Powertrain Engineering Analysis Jaguar and Land Rover Peter Jones (Academic Supervisor) School of Engineering University of Warwick Freelander 2 Intro Video: Freelander-2_Driveline_Testing.mpg J Pawar, S Biggs, R. P Jones Vehicle Dynamics and Control 2009 Cambridge University Slide 1 Agenda Freelander 2 System Architecture Vehicle Driveability Definition and Case Study CAE Approach Correlation to Test Baseline Analysis Conclusions Future Developments Questions J Pawar, S Biggs, R. P Jones Vehicle Dynamics and Control 2009 Cambridge University Slide 2
Four-Wheel Drive System Land Rover Freelander 2 System Architecture RH Front Driveshaft RH Rear Driveshaft RH Front Linkshaft Traction Coupling LH Rear Driveshaft LH Front Driveshaft J Pawar, S Biggs, R. P Jones Vehicle Dynamics and Control 2009 Cambridge University Slide 3 Vehicle Driveability Definition and Case Study Driveability is a complex attribute, the official JLR definition is: The ability to drive the vehicle smoothly, with no jerkiness or hesitation under all driving conditions, especially while shifting gear and/or controlling the accelerator pedal Introduction to Vehicle Case Study Fore-aft vehicle oscillations felt at seat-rail during cold environment testing (CET) in Sweden Oscillations induced during 70% throttle take-off on Polished Ice & Split-µ surface transition Oscillations still apparent with active systems off (HDC + ABS + TCS) Issue apparent on all Powertrain variants Test Video : Vehicle_Ice_Pullaway_Test-1.wmv J Pawar, S Biggs, R. P Jones Vehicle Dynamics and Control 2009 Cambridge University Slide 4
The Vehicle Model Non-Linear Suspension Characteristics Driveline (AWD) Powertrain System Chassis System Tyres Non-Linear Powerunit Mounting Model Rear structural flexibility Cranktrain torsional system Electronic Traction Coupling Six-Speed Manual Transmission Model Front structural flexibility Non-Linear Tyre Friction Model J Pawar, S Biggs, R. P Jones Vehicle Dynamics and Control 2009 Cambridge University Slide 5 Tyre Modelling Model based on non-linear longitudinal traction-slip ratio formulation Analytical model assumes a constant peak friction coefficient derived from the µ - λ Curves Elastic - Linear Transitional Frictional 4000 3500 3000 Tractive Force (N) 2500 2000 1500 Transition in tyre behaviour due to relaxation length neglected in model 1000 500 0 0 0.1 0.2 0.3 0.4 0.5 0.6 Wheel Slip Mu 0.85 Mu 0.18 J Pawar, S Biggs, R. P Jones Vehicle Dynamics and Control 2009 Cambridge University Slide 6
Low-µ Driveline Oscillation CAE Investigation Low-µ pullaway event replicated through full vehicle model in 1 st Gear at 70% throttle Part-load 70% throttle input applied in 1 st Gear Steady-State 70% Throttle (200Nm Engine Torque) Vehicle responses assessed with and without traction coupling active (FWD + 4WD) J Pawar, S Biggs, R. P Jones Vehicle Dynamics and Control 2009 Cambridge University Slide 7 Left to Right Split-µ Pullaway - Channel Test Data (4WD) 60 50 5.5Hz Is this due to coupling dynamics or hardware? Phase lag due to traction coupling dynamics? Higher amplitude Higher amplitude + phased oscillations oscillations seen seen on on Rear rear Driveshafts driveshafts Wheel Speed (deg/sec) 40 30 20 LHF RL RHF RR FR LHR FL RHR 10 Similar responses observed on full low-µ test 0 20 21 22 23 24 25 26 Time (sec) J Pawar, S Biggs, R. P Jones Vehicle Dynamics and Control 2009 Cambridge University Slide 8
Low-µ Pullaway - Front and Rear Torsional Response (4WD) RHF Driveshaft Low µ RHR Driveshaft Low µ 5.5Hz RHF Driveshaft High µ RHR Driveshaft High µ Difference in driveshaft torsional response reflects measured channel data (~ 5Hz) J Pawar, S Biggs, R. P Jones Vehicle Dynamics and Control 2009 Cambridge University Slide 9 Cold Environmental Test and CAE Videos CET Ice_Pullaway_Engine_View_CET_TEST.MPG CAE Ice_Pullaway_Engine_View_CAE_ANALYSIS.avi J Pawar, S Biggs, R. P Jones Vehicle Dynamics and Control 2009 Cambridge University Slide 10
4WD Heated Tarmac vs. Ice Pullaway Responses J Pawar, S Biggs, R. P Jones Vehicle Dynamics and Control 2009 Cambridge University Slide 11 4WD vs. FWD Ice Pullaway Responses J Pawar, S Biggs, R. P Jones Vehicle Dynamics and Control 2009 Cambridge University Slide 12
Shuffle Mechanism Coupling Concept - Baseline Linear Modes* Powertrain Shuffle Modes (1 6Hz) Engine Mount Modes (4-10Hz) DMF Stage 1 DMF Stage 1 DMF Stage 2 DMF Stage 2 Gear 2wd 4wd 2wd 4wd 1st 2 2.1 2.1 2.2 2nd 2.9 3.2 3.1 3.5 3rd 3.6 3.9 4.3 4.8 4th 4 4.2 5.2 5.8 5th 4.2 4.3 5.8 6.2 6th 4.3 4.4 6.1 6.4 * Linear analysis assumes High-µ surface J Pawar, S Biggs, R. P Jones Vehicle Dynamics and Control 2009 Cambridge University Slide 13 Low-µ Pullaway Effect of Powerunit Mounting Compliance Issue was thought to be related to excitation of rigid body powerunit modes Engine Mounts COMPLIANT Engine Mounts RIGID (4WD) (4WD) Fore-aft vehicle oscillations remained evident even with locked mounts J Pawar, S Biggs, R. P Jones Vehicle Dynamics and Control 2009 Cambridge University Slide 14
Low Mu Linearised Vehicle Modes 1 st Gear (4WD) 5.4 Hz Driveline Mode with Rear Halfshafts very Active Influence of Low Mu Surface on Modal Properties of System. (Not seen on Tarmac) Driveline Shuffle modes previously calculated assume efficient coupling of the vehicle inertia to the driveline torsional response via high tyre friction. Video Clip 2.5 Hz Video Clip 5.1 Hz Video Clip 5.4 Hz 7.5 Hz Power plant Pitch On low Mu surfaces the effective mass drops due to low traction, and modes and Front Halfshafts which were critically damped on tarmac can become active. Active (Not seen at this frequency on Tarmac) Video Clip 6.2 Hz Video Clip 7.5 Hz Note: Baseline Vehicle Set-Up J Pawar, S Biggs, R. P Jones Vehicle Dynamics and Control 2009 Cambridge University Slide 15 Seat-Rail Response to Modal Migration under Surface Friction Seat Rail Response to Engine Torque Input Ice vs. Tarmac (4WD Mode) Driveline Shuffle Powerunit Pitch + Front Wheel Recession (Anti-Phase) ICE TARMAC Powerunit Pitch + Front Driveshaft Torsion (In-Phase) Driveline Shuffle (Dominated by Rear Driveshaft's) J Pawar, S Biggs, R. P Jones Vehicle Dynamics and Control 2009 Cambridge University Slide 16
Seat-Rail Response to Modal Migration under Surface Friction 1 st Gear 4WD Migration of primary driveline shuffle mode Active 5.5Hz Rear Drive System torsional Mode on low friction surface J Pawar, S Biggs, R. P Jones Vehicle Dynamics and Control 2009 Cambridge University Slide 17 Powerunit Response to Modal Migration under Surface Friction Powerunit Accel. (Magnitude) Powerunit Yaw 1 st Gear 4WD 7.5Hz Powerunit Pitch Friction Coefficient Powerunit Vertical + Yaw Frequency (Hz) J Pawar, S Biggs, R. P Jones Vehicle Dynamics and Control 2009 Cambridge University Slide 18
Conclusions Measured vehicle oscillations well replicated by the analytical model Complex fighting action identified between front and rear wheels on low traction surfaces Phenomena seen to degrade both the quality of torque delivery, response and driver comfort Driveline modes seen to change with key operating parameters Dense population of chassis modes identified below 10Hz Vehicle modal responses found to be sensitive to surface friction Hardware changes identified through the vehicle model (.Hybrids) J Pawar, S Biggs, R. P Jones Vehicle Dynamics and Control 2009 Cambridge University Slide 19 Vehicle Model Correlation 2 nd Gear 70% Tarmac Tip-In 0.35 Longitudinal Seat-Rail Acceleration 0.3 Longitudinal Seat-Rail Acceleration (G) 0.25 0.2 0.15 0.1 0.05-0.05 0 16 16.2 16.4 16.6 16.8 17 17.2 17.4 17.6 17.8 18-0.1 Time (Sec) Measured CAN Frequency = 3.8Hz Vehicle Model Frequency = 3.7Hz Frequency and phase characteristics exhibit good agreement with measured vehicle accelerations Measured_DACQ Vehicle_Model J Pawar, S Biggs, R. P Jones Vehicle Dynamics and Control 2009 Cambridge University Slide 20
Future Developments Simplified non-linear models developed for system robustness studies Driveline Model Vehicle Model Vehicle system level assessments with single or multiple parameter variation Upfront conceptual studies and architecture assessment J Pawar, S Biggs, R. P Jones Vehicle Dynamics and Control 2009 Cambridge University Slide 21 Future Developments Non-Linear Model Runtimes Fully Detailed Vehicle Model (Flexible) = 9 hrs 30 mins Simplified Vehicle Model (20DoF) = 1 min 30sec J Pawar, S Biggs, R. P Jones Vehicle Dynamics and Control 2009 Cambridge University Slide 22
Questions?? J Pawar, S Biggs, R. P Jones Vehicle Dynamics and Control 2009 Cambridge University Slide 23